How humankind has changed our planet

From the formation of Earth until now, many factors have contributed to its changing state. But humankind has been a major contributor in a relatively very small period of time, as Dr Karl Kruszelnicki argues.

About four-and-a-half billion years ago, our planet slowly formed out of the primordial gas and dust of a stellar nursery, and it's been changing ever since. The main forces that have changed our planet are astronomy, geology and biology.

Examples would include (respectively) the asteroid strike that helped wipe out the non-flying dinosaurs, volcanoes and continental drift, and photosynthesis that brought oxygen into our atmosphere.

Since 1750, we have dumped about 555 billion tonnes of carbon into the atmosphere.

But now it's pretty clear that human activity is changing the planet. And one of the early big markers was how the genocide of the vast majority of humans living in the Americas led to an accidentally cooling of the Earth.

The geologists call the current epoch of time the holocene—meaning in Greek, 'totally new or recent'.

But now the geologists are beginning to talk about the need to introduce a new epoch—the Anthropocene, from 'anthrop' meaning 'people'.

Our planet is about 12,500 kilometres across, and you could fit all the humans into a box smaller than one kilometre on a side. Nevertheless, we humans have had measurable effects on the planet.

Some 50,000 to 10,000 years ago, we set off the great megafauna extinction.

About 10,000 years ago we invented agriculture—and today about 25 to 38 per cent of the world's primary productivity has been appropriated for human use.

In the early 20th Century, we invented the Haber-Bosch Process. It dragged inert nitrogen out of the atmosphere and turned it into fertiliser. It changed the 'global nitrogen cycle so fundamentally that the nearest ... geological comparison (happened) about 2.5 billion years ago'.

Each year, we humans shift about 57 billion tonnes of rock, dirt, sand, iron ore and coal, which is about three times as much as all the world's rivers shift.

Since 1750, we have dumped about 555 billion tonnes of carbon into the atmosphere.

One side-effect is that by melting ice near the poles, we have (but ever so slightly) tipped the Earth off its axis.

As another example, the global nuclear fallout from above-ground nuclear bomb tests has left a spike in carbon-14 levels back in the mid-1960s.

Even though there are now scientific peer-reviewed journals dedicated to the Anthropocene, the actual 'Anthropocene epoch' has not yet been formally ratified into the geological time scale by the International Union of Geological Sciences.

One of the requirements would be that human activity should leave markers in the geological record across the entire globe—and that these markers should be discernible for many millions of years to come.

A rather surprising event that is proposed as the start of the Anthropocene is the sudden lowering of the global carbon dioxide levels caused by the European genocide in the Americas.

Europeans arrived in the Caribbean part of the Americas in 1492, and very rapidly spread across North, Central and South America.

The population estimates are that about 55 million people were living in all of the Americas in 1492. The landscape was dominated by human activity.

For example, the Amazon was not the pristine rainforest we image. In 1542, Gaspar de Carvajal described fertile fields, roads and cities along the banks of the major rivers.

He wrote: 'There was one town that stretched for 15 miles without any space from house to house ... The land is as fertile and as normal in appearance as our Spain.'

But the invading Europeans had superior weapons technology. By a combination of war, enslavement, famine and exposure to unfamiliar diseases, the population of the Americas dropped from 55 million in 1492 to about six million by 1650. This led to a near-cessation of both fire usage and farming.

As a result, there was a natural regeneration of some half-million square kilometres of forest, grasslands and woody savanna.

The vegetation and soils dragged about 20 billion tonnes of carbon out of the atmosphere. This then caused a global decline in atmospheric carbon dioxide of about 7 to 10 parts per million—and almost certainly contributed to the Little Ice Age of the early 1600s.

This drop in carbon dioxide will be in the geological record for millions of years.

Over the last few millennia, scientific discoveries have shifted the perception that we humans are the very centre of the Universe. But the concept of the Anthropocene epoch tells us that we humans can wield truly mighty powers.

Comments (3)

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P Buddery :

27 Feb 2017 5:26:32pm

And with great power comes great responsibility. Ideally.

We are the most powerful animal in the known history of the planet, but unfortunately the people in power prefer not to exercise any responsibility. They seem to prefer to trash the place for short-term profit. What will human society be like in 1000 years as a result of this attitude? Will the few humans be cannibals fighting with bows and arrows in a wasteland devoid of other life?

I would prefer that we lived in a sustainable way, and our descendants were comfortable and safe, even if cars were to be a rarity and rampant consumerism unknown except as a warning in history books. But who cares what I think?

Jorge Nunez :

28 Feb 2017 7:03:49am

As an south american, i´m impressed to know the fact that 55 millions people lived before spaniards (our fathers) and other europeans came to america. Thanks Dr. Karl to share with us this important number of life lost.

Tom Baxter :

28 Feb 2017 9:53:25am

I think there are several indicators of the Anthropocene that would be recognized in the geological record: 1. Mass extinction of non-human life starting with the disappearance of megafauna. 2. A very thin layer of radioactive daughter products from nuclear bombs and power plants. 3. Massive amounts of people, chicken, cattle and pig fossils compared to the prior and post Anthropocene periods.